Adhesive tape

ABSTRACT

THE INVENTION RELATES TO AN ADHESIVE TAPE AND FEATURES A WEB COMPRISING A BLEND OF SHORT-FIBERED WOOD PULP, HEMP AND RAYON AND A FLEXIBLE BINDER FOR THE WEB, THE WEB BEING MICROPLEATED WITHOUT CREPING SO AS TO EFFECT LINEAR COMPACTION AND IMPART SUBSTANTIAL EXTENSIBILITY THERETO. ONE SURFACE OF THE COMPACTED WEB IS COATED WITH A PRESSURE-SENSITIVE POROUS ADHESIVE AND, PREFERABLY, THE OPPOSITE SURFACE HAS A RELEASE COATING APPLIED THERETO. THE TAPE IS USEFUL AS A FLEXIBLE AND CONFORMABLE SURGICAL TAPE.

R. N. ZIRNITE ADHESIVE TAPE July 18, 1972 qE mI @ZZQQQQOQQE led Feb. 5, 1970 United States Patent Oflice US. Cl. 117-11 Claims ABSTRACT OF THE DISCLOSURE The invention relates to an adhesive tape and features a web comprising a blend of short-fibered wood pulp, hemp and rayon and a flexible binder for the web, the web being micropleated without creping so as to effect linear compaction and impart substantial extensibility thereto. One surface of the compacted web is coated with a pressure-sensitive porous adhesive and, preferably, the opposite surface has a release coating applied thereto. The tape is useful as a flexible and conformable surgical tape.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to the field of surgical bandages and tapes which comprise a supporting web or backing, a pressure-sensitive adhesive on one side thereof and preferably a release coating on the opposite side thereof. More particularly, it relates to a low-cost surgical tape which has many of the desirable characteristics usually associated with more-costly fabric-based tapes but is made from an inexpensive blend of short fibers, including Wood pulp, hemp and rayon fibers.

While the present invention is described herein with particular reference to surgical tapes, it should be understood that the invention is not necessarily limited thereto. It can be embodied in the form of other sheetings, including masking tapes and the like, where the various desirable attributes of the present invention can be advantageously employed, as will be apparent to those skilled in the art.

Description of the prior art Previous efforts have been made to employ paper-based backings in surgical adhesive tapes to take advantage of the low cost of the wood pulp ingredient, one such effort being described in US. Pat. 3,055,496. As compared with woven fabric backings, for example, the cost savings associated with paper-based backings are substantial. As compared with non-woven fabric backings, such as disclosed in US. Pat. 3,121,021, the cost savings are not as substantial, but non-woven backings suffer from lack of uniformity, particularly with respect to strength, flexibility, tear, and the like. While paper backings have coped with the nonuniformity problem, flexibility, conformability and softness have had to be compromised to an undesired extent in order to obtain requisite strength.

It is therefore a general object of the persent invention to provide a low cost, conformable, porous surgical tape having substantially the desirable features of more costly woven and non-woven fabrics. It is another object to provide an inexpensive paper-containing tape which overcomes the flexibility and conformability problems associated with prior art paper-backed tapes. It is another object to provide a surgical tape comprising low cost 3,677,788 Patented July 18, 1972 wood pulp fibers and having enhanced tear characteristics.

It is still another object to provide an inexpensive tape which is neat, flexible, conformable, lightweight, easily handled, breathable and hypo-allergenic. It is another object to provide a surgical tape which is easy to tear when desired and yet will stretch, whereby resistance to breaking in normal use is substantially improved. These and other objects of the persent invention will become apparent as the detailed description thereof proceeds.

SUMMARY OF THE INVENTION These objects are achieved by a surgical tape comprising a specially formulated and treated web which has a pressure-sensitive porous adhesive coated on one surface and, preferably, a release coating on the opposite surface. The special formulation of the Web involves a shortfibered, randomly-dispersed blend of wood pulp, hemp and rayon fibers which are bound together by means of a flexible binder. The treatment involves linearly micropleating the web whereby substantial extensibility is imparted thereto without any substantial creping.

The wood pulp keeps the cost low; the hemp fibers introduce strength into the web; the rayon fibers, complemented by the micropleating treatment, contribute to softness, flexibility and conformability; and the shortness of the fibers impart excellent tear characteristics. Details of specific embodiments are set forth hereinafter.

The web The aforesaid web, which may have a thickness of 2 to 12 mills, or otherwise as desired, comprises a blend of about 10 to 50%, preferably about 20 to 40%, of common or paper-grade wood pulp fibers, about 5 to 40%, preferably about 10 to 30%, of Manila (abaca) hemp fibers and about 4 to 20%, preferably about 6 to 15%, of rayon fibers, all of said fibers having a length not substantially in excess of about /2 inch and preferably less than about inch, e.g., about A inch to 71 inch. The fibers are uniformly randomly dispersed throughout the web and are bound together by a flexible binder such as a soft cross-linkable rubbery binder, e.g., an acrylate binder. The binder is present in the amount of about 20 to 60%, typically about 30 to 50%. All proportions of the constituents of the web set forth above and hereinafter are weight percent based upon the finished web.

In a specific embodiment the web may have a thickness of about 4-5 mils and comprises a random blend of about 29% wood pulp fibers of about inch length, about 21% Manila (abaca) hemp fibers of about inch length, about 10% rayon fibers (a mixture of 1% and 3 denier regenerated cellulose) of about inch length and about 40% cross-linked polyethyl acrylate as the binder. Such web embodiment may be prepared by Wet process paper making techniques with the polyethyl acrylate binder being cross-linked using a diammonium phosphate catalyst.

Webs having the desired composition are commercially available. For example, Dexter paper designated type X-1574 and produced by C. H. Dexter & Sons (The Dexter Company, Windsor Locks, Conn.) has proven operable for present purposes.

Compaction of the web To impart enhanced flexibility, conformability, stretchability and softness to the web, it is subjected to a micropleating treatment so as to compact it without substantial creping. Techniques for accomplishing this treatment are known to those skilled in the art and are disclosed, for example, in US. Pats. 2,624,245 and 3,055,496.

The treatment should be sufiicient to impart a linear compaction (decrease in length with no increase in thickness) of at least about 4% (i.e., about 96% of original length), preferably about 5 to (i.e., about 95 to 90% of original length). The treatment results in an extensibility or elongation (the attribute of being stretchable without rupture and returnable upon release) of at least 8%, e.g., about 10 to of the compacted length. Results obtained when compacting Dexter paper type X-l574, using the micropleating technique of said U.S. Pat. 3,055,496 (except that no moisture is added into the web before compaction) are illustrated in the following tabulation:

Compaction at- Before After Thickness, mils 4-5 3. 5-4. 5 Basis weight, lbs/2,880 sq. ft -24 22-26 Elongation, percent (machine direct-ion) 6-7 10-15 Tensile strength, lbs/in. (machine direction). 7-9 5-9 Tear strength, grams (cross direction) 50-80 100-140 The adhesive which is applied to the compacted web can be any conventional, preferably porous, pressuresensitive adhesive used in the preparation of surgical tapes, adhesive bandages and the like, the particular type per se not being part of the present invention other than being a necessary part of the claimed construction. Suitable adhesives are, for example, the acrylate pressuresensitive adhesives presently used in surgical adhesive tape construction. Rubber-base adhesives such as those made from natural or synthetic rubber will not anchor satisfactorily to the paper. The use of a primer coating to anchor the adhesive is undesirable because it tends to overly stiffen the product.

One operable form of pressure-sensitive adhesive is a pure rubbery copolymer of isooctyl acrylate and acrylic acid in 94:6 ratio, as described in US. Pat. 2,884,126 (Re. 24,906). A technique for developing the desired and necessary microporous structure therein so as to achieve a high MVT, e.g., about 50 to 500 grams per 100 square inches in 24 hours, is described in US. Pat. 3,121,021.

Preferred formula adhesives are 2-ethylhexyl acrylatevinyl acetate copolymer or a blend of this copolymer with Z-ethylhexyl acrylate-n-tert-butyl acrylamide copolymer, the mixture cross-linked, or cured, with a suitable catalyst, e.g., Zirco dryer, a zirconium organic complex catalyst sold by Advance Solvents & Chemical. Other operable adhesives are described, for example, in U.S. Pats. 2,877,141, 2,909,278, 3,307,544 and 3,325,459.

The adhesive may be applied to the compacted web by conventional techniques, including, for example, transfer techniques, spray techniques, the use of a kissing roll, and the like. The adhesive mass is generally firmly bonded to the compacted web, no primer normally being required to anchor the mass. Volatiles may be flashed from the mass as soon as applied so that solids will not penetrate too deeply into or bleed through the compacted web.

In a typical transfer technique, the adhesive mass may be cast from a solvent on a release paper having a heatresistant, insoluble anti-stick surface, e e a silicone release coated carrier. It is passed through an oven to remove the solvent and, if necessary, to blow and cure the mass. The compacted web of the present invention is then laminated to the mass by being pressed down thereon at the end of the oven line, the release paper ultimately being stripped away.

When applying the mass by spraying, the volatiles there-. in are flashed and the mass is disposed on the compacted web in a stringy pattern. The stringy mass is anchored during the subsequent oven treatment, resulting in a highly breathable coating.

The amount of adhesive depends upon the particular adhesive, the end use of the product, and the like. In a typical surgical tape embodiment, the weight of the dry adhesive layer may be in the range of about 25 to pounds per 1000 square yards. A typical porosity (MVT) for the compacted web after application of the abovedescribed preferred adhesive may be in the range of 50 to 100 grams per 100 square inches per 24 hours.

Release coating A release coating is usually considered necessary because short-fibered, wood-pulp-containing blends have relatively low delamination or splitting resistance. Thus, in order to have a low peel force or unwind tension when unwinding the resultant tape from a roll thereof, a backsize is applied on the adhesive-free surface before, after or simultaneously with the pressure-sensitive adhesive, preferably after.

Suitable backsizes are described in US. Pat. 2,913,355, and others will be apparent to those skilled in the art and may be checked for suitability by simple experimentation. The preferred backsize comprises stearyl methacrylate acrylonitrile, suitably cured. Silicone-based backsizes, e.g., Silicolease 425 (rapid-curing release coating sold by Imperial Chemical Industries America Inc.), have been found considerably less satisfactory for present purposes.

Conventional application techniques may be employed. For example, the backsize is preferably applied by gravure roll techniques. When the backsize has a low solids content, e.g., less than about 20%, the backsize may also be sprayed on the surface of the compacted web whereby much of the solvent evaporates during the spraying, the solids concentration is increased, and little of the solids content penetrates into the web interior. As a result, the surface of the web is coated with discrete particles of the backsizing agent anchored to the web surface. As previously indicated, the backsize is preferably applied after application and curing of the adhesive mass.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more clearly understood from the following detailed description of specific embodiments read in conjunction with the accompanying drawings, wherein:

FIG. 1 illustrates in magnified cross section a fragmentary portion of the wood pulp-hemp-rayon web employed in the present invention prior to the requisite compaction thereof;

FIG. 2 is similar to FIG. 1 and illustrates the web after micropleating to effect compaction and the addition of the pressure-sensitive adhesive and backsize; and

FIG. 3 is a schematic illustrating production of the product of the present invention, including the addition of the backsize.

DETAILED DESCRIPTION OF THE DRAWINGS, INCLUDING PREFERRED EMBODIMENT Referring to FIG. 1, the starting material for the production of the present invention comprises, in a specific embodiment, web 10 having a thickness of about 5 mils and comprising a blend of about 29% wood pulp fibers 12 averaging about Vs inch in length, about 21% Manila (abaca) hemp fibers 14 averaging about 4 inch in length,

and about 10% rayon fibers 16 averaging about A inch in length, all bound together by about 40% crosslinked polyethyl acrylate binder 18. After compaction, using the micropleating technique of US. Pat. 3,055,496 (except that no moisture is added into the web before compaction), the blend of fibers appears as compacted web 20 illustrated in FIG. 2.

While the fibrous components and the web fragments depicted in FIGS. 1 and 2 are not necessarily drawn to scale, it will be noted that the thickness of the web has been reduced from about 5 mls in FIG. 1 to about 4.5 mils in FIG. 2. Likewise, the length of the web has been decreased by about 8%. As a result, the elongation or extensibility has been increased from about 6% to about 12%.

Compacted web 20 has pressure-sensitive adhesive 22, e.g., cured 2-ethylhexyl acrylate-vinyl acetate copolymer with Z-ethylhexyl acrylate-n-tert-butyl acrylamide copolymer coated on one side thereof. On the opposite side, a release coating 24, e.g., of a cross-linked blend of stearyl methacrylate acrylonitrile is applied.

A process for producing the compacted product depicted in FIG. 2 from the web depicted in FIG. 1 is illustrated in FIG. 3. Roll 26 depicts starting web 10 which may, in a specific embodiment, be Dexter paper type X-l574. As it is unwound, it passes over guide roller 28 and then down into the nip 30 formed between the unyieldable surface 32 of heated drum 34 and the yieldably-supported rubber outer surface 36 of relatively thick continuous rubber compacting belt 38. Belt 38 is held against surface 32 of drum 34 by means of nip roll 39, tensioning roll 40 and bottom guide roll 42.

As belt 38 passes over nip roll 39, its outer surface 36 follows a convex path while its inner surface follows a concave path with the result that outer surface 36 is stretched or expanded, as at C in FIG. 3. Correspondingly, as belt 38 passes the nip 30 and begins to follow the surface 32 of drum 34 instead of the surface of nip roll 39, its outer surface 36 begins to follow a concave path and accordingly shortens, or contracts, as at V in FIG. 3.

As explained in detail in connection with FIG. 4 of US. Pat. 3,055,496, because of the differences between the low coefficient of friction of surface 32 of drum 34 and the high coefiicient of friction of surface 36 of belt 38, the Web tends to stick to the contracting surface 36 and to slip on surface 32. As a result, the web is compacted longitudinally in the machine direction. Suflicient pressure is exerted with respect to the web faces to prevent crinkling or creping of the body of the web and to hold the web faces substantially flat and parallel to each other.

The life of belt 38 is enhanced by cooling it by means of water sprays 44 and 46 and, if desired, by passing the belt through water bath 48 in trough 50. Water is removed from belt 38 by means of squeeze rollers 52 and 54, which are adjusted to squeeze all but slight traces of the cooling water from the belt.

After the compacted web, now designated 20 as in FIG. 2, leaves the surface 32 of drum 34, it passes over guide roller 56 and then over positioning rollers 58, 60 and 62. The latter hold web 20 flat as it passes over radiant heater 64 which completes any necessary drying.

The preferred pressure-sensitive acrylate adhesive 66 is transferred from vessel 68 by partially-immersed transfer roll 70 to kiss roll 72, which contacts web 20 and thereby transfers the adhesive to the under-surface thereof. To prevent excessive migration of adhesive 66 into web 20, the volatile content thereof is almost immediately reduced or eliminated. This flashing operation is facilitated by infrared heaters 74 which are located adjacent kiss roll 72 and transverse the web.

The preferred backsize is sprayed on the web by nozzle means 76. Because much of the backsize solvent evaporates or flashes during the spraying, the solids concentration, which initially may be only 5 to 10%, is greatly increased and little of the solids penetrates into the compacted web. Web 20 with the adhesive coating on one side and backsize on the other side then enters curing oven 78, wherein curing temperatures, e.g., 150 to 400 F., are maintained.

The cured product is then rolled on product roll for further disposition. The cured product may be cut or sliced into any desired widths, before or after being accumulated on product roll 80, which could be a series of individual rolls. In cross section, the finished product is substantially as depicted in FIG. 2. Because wood pulp fibers predominate, it can be considered substantially a paper-backed surgical tape with many of the attributes of more-costly woven or non-woven fabrics.

From the above description, it is apparent that the objects of the present invention have been achieved. While only certain embodiments have been illustrated, many alternative modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered within the spirit and scope of the present invention and coverage thereof is intended by the claims of any patents based on this application.

Having described the invention, what is claimed is:

1. In an adhesive tape having a backing comprising a micropleated, paper-based web of randomly dispersed paper fibers and a flexible binder dispersed therethrough, said web having a pressure-sensitive adhesive coated on one surface thereof, the improvement which comprises:

(a) including in said web, randomly dispersed nonstaple length rayon fibers, said web then comprising about 10 to 50% by weight of hemp fibers, and about 4 to 20% by weight of said rayon fibers, said weight percentages based on web, all of said fibers having a length not substantially in excess of about /2-inch; and

(b) said flexible binder being in the proportions of about 20 to 60% by weight, based on web; and (c) said web being linearly micropleated without substantial creping to a length less than about 96% of its unpleated length whereby an extensibility of at least about 8% of the micropleated length is imparted thereto. 2. The adhesive tape of claim 1 wherein said flexible binder comprises cross-linked polyethyl acrylate.

3. The adhesive tape of claim 1 wherein said pressuresensitive adhesive comprises a porous acrylate pressuresensitive adhesive.

4. The adhesive tape of claim 1 wherein said pressuresensitive adhesive comprises a crosslinked blend of 2-ethylhexyl acrylate-vinyl acetate copolymer with Z-ethylhexyl acrylate-n-tert-butyl acrylamide copolymer.

5. The adhesive tape of claim 1 including a release coating on the adhesive-free surface thereof.

6. The adhesive tape of claim 5 wherein said release coating comprises stearyl methacrylate acrylonitrile.

7. In an adhesive tape having a backing comprising a micropleated paper based web of randomly dispersed paper fibers and a flexible binder dispersed therethrough, said web having a pressure-sensitive adhesive coated on one surface thereof, the improvement which comprises:

(a) including in said web randomly dispersed nonstaple length rayon fibers, said web then comprising about 20 to 40% by weight of wood pulp fibers, about 10 to 30% by weight of hemp fibers, and about 6 to 15% by weight of said rayon fibers, said weight percentages based on web, all of said fibers having a length less than about %-inch; (b) said flexible binder being in the proportion of about 20 to 60% by weight based on web; and

(c) said web being linearly compacted without substantial creping to about 95 to of its original length, whereby an extensibility of about 10 to 15% of the compacted length is imparted thereto.

8. The adhesive tape of claim 7 wherein said flexible binder is a cross-linked polyethyl acrylate.

7 8 9. The adhesive tape of claim 7 wherein a stearyl meth- 2,937,109 5/ 1960 Bartell et a1. 117-122 acrylate acrylonitrile release coating is provided on the 3,055,496 9/1962 Dunlap 11760 X other surface of said web. 3,114,670 12/1963 Iwasaki 162146 10. The adhesive tape of claim 7 wherein said pressure- 3,121,021 2/ 1964 Copeland 128-156 X sensitive adhesive comprises a crosslinked blend of 2- 5 3,307,544 3/1967 Gander et a1 11747 X ethylhexyl acrylate-vinyl acetate copolymer with Z-ethyl- 3,325,459 6/ 1967 Gander 260-805 X hexyl acrylate-n-tert-butyl acrylamide copolymer.

WILLIAM D. MARTIN, Primary Examiner Refe'ems Cited B. D. PIANALTO, Assistant Examiner UNITED STATES PATENTS 10 2,624,245 1/1953 Cluett 162--206 UX 2,877,141 3/1959 Shelley et a1 117122 117'68.5, 122 P, 122 P BU, 155 -UA; 162--141, 146 

